Mis-chi-vus.
And I stand by mis-chee-vee-us being plain old wrong. Some folks just can’t admit they’re wrong. Thus arguments regarding dialect and idiolect and soforth.
But all you have to do in this case is look at how the word is spelled: mischievous
People rush through and the ie pairing throws them off and they pronounce what they think they see. Easy fix.
When I informed my wife that the L in salmon is silent she was stubborn at first, next embarrassed and now it’s sa-mun. She’s not dumb, never has been. Just not informed.